Serotonin (also referred to as 5-hydroxytryptamine or 5-HT) is a neurotransmitter that has been strongly implicated in the pathophysiology and treatment of a wide variety of neuropsychiatric disorders. Serotonin exerts its effects through a diverse family of serotonin receptor molecules (referred to herein as “5-HT receptors” or “5-HTRs”). Classically, members of the serotonin receptor family have been grouped into seven (7) subtypes pharmacologically, i.e., according to their specificity of various serotonin antagonists. Thus, while all the 5-HT receptors specifically bind with serotonin, they are pharmacologically distinct and are encoded by separate genes. To date, fourteen (14) mammalian serotonin receptors have been identified and sequenced. More particularly, these fourteen separate 5-HT receptors have been grouped into seven (7) pharmacological subtypes, designated 5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6, and 5-HT7. Several of the subtypes are further subdivided such that the receptors are grouped pharmacologically as follows: 5-HT1A, 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3A, 5-HT3B, 5-HT4, 5-HT5A, 5-HT6, 5-HT7. However, when the nucleic and amino acid sequences of the receptors are compared, the percent identity among the subtypes is not correlated to the pharmacological groupings.
Of the fourteen different mammalian serotonin receptors that have been cloned, all but one are members of the G-protein coupled receptor superfamily. Serotonin receptors 5-HT1A, 5-HT1B, and 5-HT1D inhibit adenylate cyclase, and 5-HT2 receptors activate phospholipase C pathways, stimulating breakdown of polyphosphoinositides. The 5-HT2 receptor belongs to the family of rhodopsin-like signal transducers that are distinguished by a seven-transmembrane configuration and functional linkage to G-proteins. The 5-HT3 receptor family includes ligand-gated ion channel receptors that have four putative TMDs.
Serotonin regulates a wide variety of sensory, motor and behavioral functions in the mammalian CNS, including behaviors such as learning and memory, sleep, thermoregulation, motor activity, pain, sexual and aggressive behaviors, appetite, neuroendocrine regulation, and biological rhythms. Serotonin has also been linked to pathophysiological conditions such as anxiety, depression, obsessive-compulsive disorders, schizophrenia, suicide, autism, migraine, emesis, alcoholism and neurodegenerative disorders. This biogenic amine neurotransmitter is synthesized by neurons of the brain stem that project throughout the CNS, with highest density in basal ganglia and limbic structures (Steinbusch, 1984, In: Handbook of Chemical Neuroanatomy 3:68-125, Bjorklund et al., Eds., Elsevier Science Publishers, B. V.).
Studies have suggested that serotonin may play a role in the immune system since data demonstrate that serotonin receptors are present on various cells of the immune system. There have been reports in the literature about the immunomodulatory effects of adding serotonin exogenously to mitogenically stimulated lymphocyte cultures. Under some circumstances, serotonin has been shown to stimulate the activated T cells (Foon et al., 1976, J. Immunol. 117:1545-1552; Kut et al., 1992, Immunopharmacol. Immunotoxicol. 14:783-796; Young et al., 1993, Immunology 80:395-400), whereas other laboratories report that high concentrations of added serotonin inhibit the proliferation (Slauson et al., 1984, Cell. Immunol. 84:240-252; Khan et al., 1986, Int. Arch. Allergy Appl. Immunol. 81:378-380; Mossner & Lesch, 1998, Brain, Behavior, and Immunity 12:249-271).
Of the fourteen known pharmacologically distinct serotonin receptors, lymphocytes express type 2A, type 2B, type 2C, type 6 and type 7 on resting cells (Ameisen et al., 1989, J. Immunol. 142:3171-3179; Stefulj et al., 2000, Brain, Behavior, and Immunity 14:219-224) and that the type 1A and type 3 receptors are up-regulated upon activation (Aune et al., 1993, J. Immunol. 151:1175-1183; Meyniel et al., 1997, Immunol. Lett. 55:151-160; Stefulj et al., 2000, Brain, Behavior, and Immunity 14:219-224).
The involvement of the 5-HT1A receptors in human and murine T cells has also been demonstrated (Aune et al., 1990, J. Immunol. 145:1826-1831; Aune et al., 1993, J. Immunol. 151:1175-1183; Aune et al., 1994, J. Immunol. 153:1826-1831). These studies established that IL-2-stimulated human T cell proliferation could be inhibited by a blockade of tryptophan hydroxylase, i.e., the first enzyme involved in the conversion of tryptophan to serotonin, and that the inhibition could be reversed by the addition of 5-hydroxy tryptophan. Furthermore, human T cell proliferation was blocked in vitro with a 5-HT1A-specific receptor antagonist. In a murine model, a type 1A receptor antagonist, but not a type 2 receptor antagonist, was able to inhibit the in vivo contact sensitivity response, but not antibody responses, to oxazalone.
PCT Publication No. WO 03/106660 discloses the use of fluphenazine, an antagonist of 5-HT(1B/1D) and 5-HT(2C) receptors, for inhibiting proliferation and inducing cell death in lymphocytes.
There exists a long-felt need to develop novel compounds and therapies for treating diseases related to activated lymphocytes and lymphocyte proliferation, especially diseases related to activated T cells and B cells. In addition, there is a long-felt need to develop novel compounds without the side effects related to other serotonin receptor antagonists. The present invention meets these needs.